U.S. patent number 5,061,079 [Application Number 07/491,596] was granted by the patent office on 1991-10-29 for stirrer.
This patent grant is currently assigned to Satake Chemical Equipment Mfg., Ltd.. Invention is credited to Katsumi Shiobara.
United States Patent |
5,061,079 |
Shiobara |
October 29, 1991 |
Stirrer
Abstract
A stirrer for stirring a liquid in a container, which includes a
stator; a rotor disposed in the container and provided with
stirring vanes; and a cylindrical housing of nonmagnetic material
having a peripheral wall thereof interposed between the stator and
rotor and rotatably supporting the rotor through intervention of
the liquid. This arrangement provides a stirrer of simple and
compact construction, which can stir the liquid in a container
completely in a closed state free of sliding portions of rotary
components or shaft seal portions.
Inventors: |
Shiobara; Katsumi (Yono,
JP) |
Assignee: |
Satake Chemical Equipment Mfg.,
Ltd. (Moriguchi, JP)
|
Family
ID: |
27522659 |
Appl.
No.: |
07/491,596 |
Filed: |
March 12, 1990 |
Foreign Application Priority Data
|
|
|
|
|
Mar 10, 1989 [JP] |
|
|
1-59150 |
Mar 15, 1989 [JP] |
|
|
1-62685 |
Apr 4, 1989 [JP] |
|
|
1-84098 |
Apr 5, 1989 [JP] |
|
|
1-86044 |
Apr 25, 1989 [JP] |
|
|
1-47738 |
|
Current U.S.
Class: |
366/127;
91/DIG.4; 366/273; 366/274 |
Current CPC
Class: |
B01F
13/0827 (20130101); B01F 13/0872 (20130101); B01F
13/0863 (20130101); B01F 15/00688 (20130101); B01F
13/0845 (20130101); Y10S 91/04 (20130101) |
Current International
Class: |
B01F
15/00 (20060101); B01F 13/08 (20060101); B01F
13/00 (20060101); B01F 013/08 () |
Field of
Search: |
;366/273,274,127,241,244,349 ;91/DIG.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trafton; David
Assistant Examiner: Rhoa; Joseph A.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt
Claims
What is claimed as new and desired to be secured by letters patent
of the United States is:
1. A stirrer for stirring a liquid, which comprises:
a container within which said liquid is housed and which is mounted
on a base;
a stator positioned on said base and located within said
container;
a rotor disposed in said container and provided with stirring
vanes;
a cylindriaclly shaped housing of nonmagnetic material having a
peripheral wall thereof interposed between said stator and said
rotor and fluidically rotatably supporting said rotor by said
luquid, wherein said stator is located within said housing, and
said rotor is in the shape of a cap having stirring vanes on an
outer surface thereof and having an aperture in a top wall thereof,
said rotor being rotatably fitted on said housing so as to form a
small gap between an inner periphery of said rotor and said
housing; and
a plurality of radially extending grooves formed on one of an inner
surface of a top wall of said rotor and a top surface of said
housing, wherein a surface is formed contiguously to each of said
grooves in such a manner as to narrow the gap between said inner
surface of the top wall of said rotor and said top surface of said
housing in a circumferential direction.
2. A stirrer as defined in claim 1, wherein said tator has a
plurality of windings wrapped around a circumferential part
thereof.
3. A stirrer as defined in claim 1, wherein said housing comprises
an indented part of a bottom wall portion of said contaienr.
4. A stirrer as defined in cliam 1, wherein said surface formed
contiguously to each one of said grooves comprises a stepped
surface.
5. A stirrer as defined in cliam 1, wherein said surface formed
contiguously to each one of said grooves comprises a sloped
surface.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a stirrer which is useful particularly in
pharmaceutical, food and chemical industries for mixing,
dissolving, kneading and diffusing a liquid or other material in a
container.
2. Discussion of the Background
Illustrated in FIG. 30 is a known mixer which is provided with a
stirring vessel a, a rotational transmission c located externally
under the bottom wall of the stirring vessel a and driven from an
electric motor b, and an impeller shaft e which protrudes from
below into a lower portion of the vessel a and having impeller
vanes d. The impeller shaft e and the transmission c are coupled to
each other through a magnetic coupling f to rotate the impeller
wheel d.
This sort of conventional stirrer is required to separately provide
a rotational drive like the motor b for rotating the impeller vanes
d which invariably have drawbacks in that they are of complex
construction and are large in size.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a stirrer which
is capable of stirring a liquid in a container in a completely
closed state with no slide portions of rotary components nor a
shaft seal portion being required.
It is another object of the invention to provide a stirrer which is
compact construction and is reduced in size.
In accordance with the present invention, the foregoing objects are
achieved by the provision of a stirrer for stirring a liquid in a
container, which essentially includes a cylindrical housing of
nonmagnetic material having the peripheral wall portion thereof
interposed between a stator and a rotor with stirring vanes for
supporting the rotor rotatably through intervention of the liquid
from the container.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the
attendant advantages thereof will be readily obtained as the same
becomes better understood by reference to the following detailed
description when considered in connection with the accompanying
drawings, wherein:
FIG. 1 is a plan view of a first embodiment of the invention;
FIG. 2 is a front view of the embodiment of FIG. 1;
FIG. 3 is a cross-sectional view taken on line III--III of FIG.
2;
FIG. 4 is a perspective view of a rotor;
FIG. 5 is a plan view of a second embodiment of the invention;
FIG. 6 is a partly cutaway front view of the embodiment of FIG.
5;
FIG. 7 is a partly cutaway plan view of a third embodiment of the
invention;
FIG. 8 is a partly cutaway front view of the embodiment of FIG.
7;
FIG. 9 is a plan view of a fourth embodiment of the invention;
FIG. 10 is a vertical section of a fifth embodiment of the
invention;
FIG. 11 is a sectional view taken on line XI--XI of FIG. 10;
FIG. 12 is a sectional view taken on line XII--XII of FIG. 11;
FIG. 13 is a view similar to FIG. 12 but showing a sixth embodiment
of the invention;
FIG. 14 is a vertical section of a rotor of a seventh embodiment of
the invention;
FIG. 15 is a vertical section of a rotor of an eighth embodiment of
the invention;
FIG. 16 is a vertical section of a ninth embodiment of the
invention;
FIG. 17 is a vertical section of a tenth embodiment of the
invention;
FIG. 18 is an enlarged sectional view taken on line XVIII--XVIII of
FIG. 17;
FIG. 19 is a vertical section of a rotor;
FIG. 20 is a vertical section of a modification of the stirrer of
the tenth embodiment arranged in the fashion of the ninth
embodiment;
FIG. 21 is a partly cutaway sectional view of an eleventh
embodiment of the invention;
FIG. 22 is a partly cutaway sectional view of a twelfth embodiment
of the invention;
FIG. 23 is a partly cutaway sectional view of a thirteenth
embodiment of the invention;
FIG. 24 is a vertical section of a fourteenth embodiment of the
invention;
FIG. 25 is a partly cutaway sectional view of a fifteenth
embodiment of the invention;
FIG. 26(a) and (b) are diagrammatic views explanatory of the
operation of the rotor in the fifth to fifteenth embodiments;
FIG. 27 is a vertical section of a sixteenth embodiment of the
invention;
FIG. 28 is a cross-sectional view of a stator;
FIG. 29(a)through (e) are diagrammatic views explanatory of the
operation of the rotor; and
FIG. 30 is a partly cutaway elevation of a conventional
stirrer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, the invention will be described more particularly, firstly by
way of the first embodiment shown in FIGS. 1 through 4.
In these figures, indicated at 10 is a rectangular liquid container
and at 1 is a cylindrical housing of a nonmagnetic material which
is projectingly provided in a lower portion of one side wall of the
liquid container 10. The housing 1 is hermetically closed at
opposite ends thereof, and provided with first communication ports
11a at opposite end portions of the peripheral wall thereof and a
second communication port 11b in a center portion of the peripheral
wall. Thus, the housing 1 is communicable with the liquid container
10 through the just-mentioned first and second communication ports
11a and 11b. Received in the housing 1 is a hollow cylindrical
rotor 3 which is open at the opposite ends and which leaves a small
clearance or gap g therearound as shown in FIG. 3. The rotor 3 has
cylindrical opposite end portions 3a which comprise a coated
magnetic material such as SS41 or the like and a conductive body of
copper, aluminum or the like, as well as a cylindrical center
portion 3b which is constituted by stainless steel, engineering
plastics or the like. As shown in FIGS. 3 and 4, a large number of
inclined openings or slots 3c are provided in the center portion 3c
to function as a stirring portion. The rotor 3 as a whole is coated
with Teflon or other corrosion-resistant material.
Rotating field devices, namely, stators 2, are located on the outer
side of the housing 1 opposingly to the cylindrical end portions 3a
of the rotor 3. In this instance, each one of the stators 2 is
constituted by a multi-layered iron core of silicon steel sheets or
the like and a winding wound around the core.
With the above-described arrangement, rotating fields are induced
in the cylindrical portions 3a of the rotor 3 as soon as current is
conducted through the stator 2, whereupon the liquid is drawn into
the gap g by the rotor 3 to produce a bearing effect, rotating the
rotor 3 smoothly in a noncontacting state in the direction of arrow
A in FIG. 3 by the balancing action between the attraction of the
rotating fields and gravity acting on the rotor 3. At this time,
since the rotor 3 is provided with the slots 3c in the center
portion 3b, the liquid which flows in through the first
communicating ports 11a of the housing 1 is sucked into the rotor 3
through the openings at the opposite ends thereof, while the liquid
in the rotor 3 is stirred as it is discharged through the slots 3c
to return to the container 10 through the second communication port
11b. This is repeated to stir the liquid in the container 10.
Referring now to FIGS. 5 and 6, there is shown a second embodiment
of the invention which employs a vertical type cylindrical liquid
container 10 with a rectangular open frame 11c projecting from a
lower portion of its side wall, and a cylindrical housing 1 fixedly
connected in a hermetically sealed state to the frame 11c along the
edges of a rectangular opening formed on one side of the housing 1.
In the same manner as in the foregoing first embodiment, upon
rotating the rotor 3 by supplying current to the stator 2, the
liquid flowing toward the opposite end portions of the open frame
11c from the container 10 is sucked into the openings at the
opposite ends of the rotor 3 and then discharged through the slots
3c into the center portion of the open frame 11c to return to the
container 10. The liquid in the container 10 is thus stirred by
repeated circulation through the rotor 3. This embodiment has an
advantage in that the housing 1 is easily detachable from the
container 10 to facilitate their transportation or maintenance and
service.
FIGS. 7 and 8 illustrate a third embodiment of the invention, which
employs a vertical type cylindrical liquid container 10 with a
housing 1 hermetically and integrally connected to an opening in
the side wall of the container 10 for effective use of the
installation space. This embodiment is suitable for application,
particularly in a case where only a limited floor space is
available, and can perform the stirring operation in substantially
the same manner as the foregoing second embodiment.
Shown in FIG. 4 is a fourth embodiment of the invention, wherein a
housing 1 is spaced more from a container 10 than in the
above-described second embodiment and communicated with the latter
through three ducts 11d, more specifically, a couple of side ducts
11d and a center duct 11d. The stirring operation is substantially
the same as in the first embodiment. With this fourth embodiment,
the stator 2 can circumvent the rotor 3 to a greater degree to
enhance the rotational efficiency.
Referring to FIGS. 10 to 12, there is shown a fifth embodiment of
the invention, which is of a type having a housing 1 formed within
an indented bottom wall portion of a stirring container 10. More
specifically, the housing 1 is formed of a nonmagnetic material at
least in those portions which oppose the rotor 3 as will be
described hereinafter, and in this case formed by an indented
portion which is provided in a center portion of the bottom wall of
the container 10 in such a manner as to circumvent the stator 2.
Denoted at 3 is a rotor which is formed in a cap-like shape and
which has its peripheral wall portion formed of a magnetic material
such as SS41 or the like and a conducting body of copper, aluminum
or the like. The top wall of the rotor 3 is formed of stainless
steel, engineering plastics or the like. The rotor 3 as a whole is
coated with a corrosion-proof material sold under the TEFLON
trademark. The rotor 3 is fitted on the housing 1 which circumvents
the stator 2, and is provided with an aperture 3d at the center of
its top wall and with a plurality of stirring vanes 3e on the
peripheral and top wall surfaces. As shown particularly in FIGS. 11
and 12, a plurality of radial strip-like grooves 4 are cut into the
inner surface 3f of the top wall of the rotor 3 at uniform angular
intervals in the circumferential direction. Each groove 4 is
connected to stepped surfaces 5a to 5c of a sectoral shape.
Indicated at 6 is a fixed base for mounting the housing 1 and
stator 2.
This embodiment operates as follows.
Upon supplying current to the stator 2 to produce shifting fields,
the rotor 3 is rotationally driven in the direction of arrow X for
stirring the liquid A with the vanes 3e on the rotor 3.
In this instance, since the rotor 3 is provided with aperture 3d at
the center of its top wall, the liquid A which is urged to flow
into the grooves 4 through the aperture 3d by rotation of the rotor
3 is firstly supplied to the peripheral portions of the respective
grooves 4. As the liquid proceeds successively from the first to
third sectoral stepped surfaces 5a to 5c, the liquid pressure is
increased stepwise, producing a pressure which acts upwardly on the
rotor 3 to float the same upward, while part of the liquid A is
forced to flow downward through the small gap g between the housing
1 and rotor 3.
In this manner, the gap g is constantly maintained and the rotor 3
is rotated smoothly in a balanced state with the reaction forces of
the top stirring vanes 3e and circumferential stirring vanes
3e.
As is clear from the foregoing description, the stirring apparatus
of this embodiment employs a noncontacting rotor for the stirring
operation, so that it can be applied to either a sealed or
nonsealed type container and facilitates stirring operations under
high pressure or in a vacuum, free of abrasive wear as would result
from sliding movements and free from the generation of vibrations.
Moreover, the liquid A in the container 10 can be discharged more
easily after stirring operation.
Referring to FIG. 13, there is illustrated a sixth embodiment of
the invention, in which the stepped surfaces 5a to 5c of the
foregoing fifth embodiment are replaced by an infinite number of
stepped surfaces, namely, by a linearly inclined surface 5c to
obtain the same effects as in the fifth embodiment.
Illustrated in FIG. 14 is a seventh embodiment of the invention, in
which stepped surfaces 5e to 5g are formed on the rotor 3 in the
circumferential direction and concentrically in a manner so as to
minimize the gap toward the outer periphery. FIG. 15 shows an
eighth embodiment in which the number of the stepped surfaces 5e to
5g is increased infinitely to present a linearly inclined surface
5h. In the seventh and eighth embodiments, the liquid which is
urged to flow into the aperture 3d by rotation of the rotor 3 is
forced outward in the gap between the top wall of the rotor 3 and
the top surface of the housing 1 under the influence of the
centrifugal force. Since the gap is narrowed toward the outer
periphery, the liquid pressure is increased outwardly, generating a
pressure which pushes up the rotor 3 into a floating state for
smooth rotation.
Although the grooves and stepped surfaces are formed on part of the
rotor 3 in the fifth to eighth embodiments, they may be formed on
the top surface of the housing 1 if desired.
Shown in FIG. 16 is a ninth embodiment of the invention, in which a
closed type housing 1 of a nonmagnetic material is formed
separately from the container 10 for the liquid A, and receives
therein a stator 2. A rotor 3 is fitted on the housing 1, and
grooves and stepped surfaces or a linearly inclined surface are
formed on the inner surface of the top wall of the rotor or on the
top surface of the housing 1 as in the fifth to eighth embodiments.
This stirrer can be placed in an ordinary container. Reference
number 7 indicates a lead wire.
Referring to FIGS. 17 to 19, there is illustrated a tenth
embodiment of the invention, wherein pumping vanes 3g which are
curved in the circumferential direction are projectingly provided
on the inner surface of the top wall of a rotor 3 as shown
particularly in FIGS. 18 and 19. In addition, a number of
labyrinths 8 are formed on the inner periphery at the lower end of
the peripheral wall of the rotor 3.
Thus, supplying current to the stator 2 to generate shifting fields
which drive the rotor 3 to rotate in the direction of arrow X, the
liquid A which is urged to flow into the gap between the opposing
surfaces of the rotor 3 and the housing 1 through the aperture 3d
is forcibly pushed outward by the pumping vanes 3g on the inner
surface 3f of the top wall of the rotor 3 with an outwardly
increasing liquid pressure to push up the rotor 3 before flowing
down through the gap between the opposing peripheral wall surfaces
of the housing 1 and rotor 3. Due to the existence of the
labyrinths 8 at the lower end of the rotor 3, downward flow of the
liquid A is blocked there to a substantial degree so as to float
the rotor 3 upward securely while in rotation. Accordingly, the
rotor 3 is rotated smoothly, balancing with the reaction forces of
the stirring vanes 3e on its peripheral wall, and consequently the
liquid A is stirred by the vanes of the rotor 3.
Although the pumping vanes 3g are provided on part of the rotor 3
in this embodiment, of course they may be formed on the top wall of
the housing 1.
Further, the labyrinths 8 which are formed on the inner peripheral
surface at the lower end of the rotor 3 may be provided at an
intermediate portion on the inner periphery of the rotor 3 or on
the outer peripheral surface of the housing 1 if desired.
Moreover, instead of forming the housing 1 by part of the container
10 as in the present embodiment, a closed type housing 1 may be
formed separately from the container 10 as shown in FIG. 20 in a
manner similar to the ninth embodiment, receiving a stator 2 in the
housing 1 and fitting a rotor 3 over the housing 1. In this case,
pumping vanes 3g are provided either on part of the rotor 3 or on
the opposing surface of the top wall of the housing 1. Further,
labyrinths 8 may be provided on the rotor 3 or on the opposing
peripheral surface of the housing 1.
Referring to FIG. 21, there is shown an eleventh embodiment of the
invention, in which a housing 1 is fixed by screws to a lower
portion of a stirring container 10 through an O-ring 9a or other
suitable seal member. Indicated at B is an incompressible fluid in
liquid form which is filled in the housing 1 and in the gap space
around a stator 2. Lead wire 7 from the stator 2 is passed through
a seal 9b. Thus, when the container 10 is under high pressure, the
compressive force which acts on the housing 1 through the liquid A
is sustained by the incompressible fluid B filled in the housing 1.
It follows that the wall thickness of the housing 1, particularly,
the thickness of the peripheral wall portion can be reduced to
enhance the efficiency of the motor.
Illustrated in FIG. 22 is a twelfth embodiment of the invention, in
which a housing 1 is suspended from the top wall of a stirring
container 10 by means of a hollow cylindrical support member 12.
The housing 1 is in communication the cylindrical support member 12
which is filled with an incompressible fluid B. A seal 9b is
provided at the upper end of the support member 12. In this
embodiment, the rotor 3 is formed in C-shape in section.
The incompressible fluid B may be filled in the housing 1 alone,
locating the seal 9b in the position indicated by broken line in
FIG. 22.
FIG. 23 shows a thirteenth embodiment of the invention, in which a
communication hole 13 is formed in an upper portion of a hollow
cylindrical support member 12 and the fluid B is filled in a
housing 1 and only in lower portion of the support member 12,
leaving an empty space thereabove. Accordingly, when stirring the
container 10 under high pressure, the upper empty space in the
support member 12 is raised to the same pressure level by
communication with the upper empty space in the container 10
through the communication hole 13, as a result zeroing on
equalizing the pressure difference between inside and outside of
the housing 1 and the cylindrical support member 12. This permits a
reduction in their wall thicknesses so as to enhance the motor
efficiency.
Alternatively, the hollow spaces in the casing 1 and support member
12 may be entirely emptied and filled with the high pressure gas in
the upper space of the container 10 by communication therewith
through the communication port 13, instead of the fluid B.
Although a situation where a high pressure prevails in the
container 10 has been described as an example in each one of the
foregoing eleventh to thirteenth embodiments, there occurs almost
no pressure difference between inside and outside of the housing 1
even under low pressure or vacuum condition, permitting a reduction
in the wall thickness of the housing 1. The housing 1 which has
been shown as being fixed in the container 10 in the eleventh to
thirteenth embodiments may be provided as an independent closed
type which can be set in an arbitrary position within an existing
container.
Referring to FIG. 24, there is illustrated a fourteenth embodiment
of the invention, wherein a pipe 14 is inserted in a center
aperture of a stator 2 to form an air passage 15. The lower end of
the pipe 14 is passed through and fixed to a support plate 16 which
supports the container 10, the side walls of the pipe 14 being
spread into a trumpet-like shape under the support plate 16 to
accommodate a fan 17. Indicated at 18 are openings which are formed
in the support plate 16, namely, in the bottom wall of the housing
1 beneath the peripheral wall portions of the stator 2, and
indicated at 19 are legs which support the container 10.
Upon generating shifting fields by supplying current to the stator
2, the rotor 3 is rotated on the liquid bearing which is formed in
the small clearance between the rotor 3 and the housing 1, stirring
the liquid A with the vanes 3e which are provided on the rotor 3.
As the fan 17 is actuated, the air which is drawn by the fan 17 is
sent into the air passage 15 and circulated through the housing 1
and along the peripheral wall portions of the stator 2 before being
discharged through the openings 18. As a result of this air
circulation, the housing 1 is cooled and the stator is smoothly
rotated so as to stir the liquid A efficiently.
By reversing the rotation of the fan 17, the air circulation can be
changed so as to draw air through the openings 18 and discharge it
through the air passage 15.
Shown in FIG. 25 is a fifteenth embodiment of the invention, in
which a housing 1 is provided in an upper portion of a container 10
and supported on a tubular support member 20 which is pendant from
the top wall of the container 10. A pipe 14 is inserted centrally
in the support member 20. The lower end of the pipe 14 is fitted in
the center hole of the stator 2, while the upper end is spread into
a trumpet-like shape to accommodate a fan 17. This embodiment
operates in the same manner as the foregoing fourteenth
embodiment.
Instead of employing an air-cooled type stator 2 as in the
fourteenth and fifteenth embodiments, arrangements may be made to
cool the stator by feeding thereto cooling water or other cooling
liquid with the use of a pump.
In any of the foregoing fifth to fifteenth embodiments, there may
arise the following problem in a situation where the winding is
wrapped around the entire circumference of the stator 2.
Namely, as power is supplied to the winding of the stator 2, an
attracting force F.sub.1 is generated in a certain direction by the
magnetic field of the winding as shown in FIG. 26a, exerting a
pulling force on the rotor 3 and producing on the outer side of the
housing 1 a liquid film of a wedge-like shape in the direction of
rotation. As a result, the liquid between the rotor 3 and housing 1
is pulled in due to its viscosity and generates a liquid pressure
with an overall reaction force F.sub.2 in the opposite direction.
By vector addition of the attracting force F.sub.1 and the reaction
force F.sub.2, a combined force F.sub.3 acts on the peripheral wall
in the rotational direction. Consequently, as shown in FIG. 26b,
the rotor is pulled in the direction of the combined force F.sub.3,
and in this state the attracting force F.sub.1 and overall reaction
force F.sub.2 of the liquid pressure occur in the manner as
described hereinabove. Therefore, next the rotor 3 is pulled in the
direction of the combined force of the attracting force F1.sub.1
and overall reaction force F.sub.2. Since the stator 2 has the
winding wrapped 360.degree. around its entire circumference, the
position where the rotor 3 approaches the housing 1 is shifted
sequentially, putting the rotor 3 into eccentric rotational motions
and sometimes causing the rotor 3 to hit against the circumference
of the housing 1. This makes it difficult to ensure smooth rotation
of the rotor.
In order to overcome this problem, the sixteenth embodiment shown
in FIGS. 27 and 28 has stator windings 2A, 2A'; 2B, 2B' and 2C, 2C'
wrapped over an angle of 150.degree. in slots 2a, 2a'; 2b, 2b' and
2c, 2c'. Upon supplying current to the windings 2A, 2A'; 2B, 2B'
and 2C, 2C', shifting fields are generated in the stator 2 and
thereby the rotor 3 on the opposite side of the housing 1 is urged
to rotate in the direction of arrow W and at the same time pulled
toward stator 2. As a result, the rotor 3 is moved into an
eccentric position as shown in FIG. 29a, forming a small gap
g.sub.0 between the rotor 3 and housing 1 with a fluid bearing
constituted by the inflowing liquid film. The overall force P.sub.1
of the attracting forces Pa.sub.1 to Pz.sub.1 of the stator
windings acts on the rotor 3 across the small gap g.sub.0 in the
direction of <.alpha. short of the small gap position. At this
time, pressures Pa.sub.2 to Pz.sub.2 of the wedge-shaped liquid
film act on the rotor 3 and housing 1, and their overall pressure
P.sub.2 acts as shown in FIG. 29b. Accordingly, the combined vector
force P.sub.3 of the overall attracting force P.sub.1 and the
overall pressure P.sub.2 acts on the rotor 3 as shown in FIG. 29c,
shifting the small gap g.sub.0 through an angle of .theta. to
g'.sub.0. In this state, the small gap g'.sub.0 is located in the
vicinity of the end of the stator windings where the attracting
forces P'a.sub.1 to P'z.sub.1 of the windings are interrupted in
the direction of the rotation as shown in FIG. 29d. Therefore, the
overall attracting force P'1 is maintained substantially in the
same direction as the aforementioned overall force P.sub.1.
However, as a result of the shift of the small gap from g.sub.0 to
g'.sub.0, the overall pressure P'.sub.2 is shifted in the direction
of rotation as shown in FIG. 29e. Therefore, the combined vector
P'.sub.3 of the overall attracting force P'.sub.1 and the overall
pressure P'.sub.2 are almost extinguished as shown in FIG. 29c to
maintain a constant small gap g'.sub.0, while the rotor 3 is
rotated by the shifting fields of the stator windings. Thus, the
rotor 3 tends to move into the eccentric position to form a narrow
gap g.sub.0 only through a rotational angle of 150.degree. where it
is associated with the windings 2A, 2A' to 2C, 2C', and the
eccentric displacement does not occur through the remaining angle
of rotation. Namely, as the rotor 3 continues its rotation, the
eccentric circular movements due to the eccentric displacement are
extinguished so as to allow the rotor to smoothly rotate while
keeping a constant gap g'.sub.0 from the housing and efficiently
stirring the liquid A with the vanes 3e.
The stator windings 2A, 2A' to 2C, 2C' may be increased or reduced
suitably to cover an arbitrary rotational angle, for example, to
cover an angle of 180.degree. or 120.degree. if desired.
Needless to say, the rotor can be more smoothly rotated in the
fifth to fifteenth embodiments by adopting the partial wrapping of
the windings as in the sixteenth embodiment.
Obviously, numerous modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *